20191212 Preliminary Drainage Report.pdfPreliminary Drainage Report
Sundstone SP
for
Sundstone HOA
Attn: Lindell Graham
1414 9th Ave N, Apt. 301
Edmonds, WA 98020
206.717.2995
SITE LOCATION:
1414 9th Ave N, Apt. 301
Edmonds, WA 98020
Tax Parcels, 00427800100100,...100200,...100300,
... 200200,...200300,...200400,...200500, 300100,
... 300500
A6 M 0&
**McF It
3B 5 4� *
Prepared by:
Joseph M. Smeby, P,E.
Job No: 19-0117
June, 2019
Revised: Dec. 2019
100400,...100500,...200100,
300200,...300300,...300400,
TABLE OF CONTENTS
TABLEOF CONTENTS .......................................................................................................................... I
LISTOF FIGURES .................................................................................................................................. 2
1. INTRODUCTION & SITE CLASSIFICATION .................................................................................... 3
2. STORMWATER SITE PLAN ........................................................................................................... 4
3. SWPPP NARRATIVE ..................................................................................................................... 4
A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT .............................................................. 5
B. SWPPP MINIMUM ELEMENTS ..................................................................................................... 5
4. WATER POLLUTION SOURCE CONTROL ...................................................................................... 7
5. PRESERVATION OF NATURAL DRAINAGE SYSTEM ...................................................................... 7
6. ON -SITE STORMWATER MANAGEMENT ........................................................................... ......... 7
7. RUN-OFF TREATMENT ................................................................................................................ 9
8. FLOW CONTROL ........................................................................... .... ........................................... 9
9. WETLANDS PROTECTION ............................................................................................................ 9
10. OPERATIONS AND MAINTENANCE MANUAL .............................................................................. 10
APPENDIX A - To be provided with final engineering report at time of construction plan
submittal.
Sundstone SP 19-0117
October, 2019 Page 1
LIST OF FIGURES
ITEM PAGE
FIGURE1 VICINITY MAP ..... ................................................................................. 10
FIGURE 2 EXISTING DRAINAGE BASIN MAP ...................................................... 11
FIGURE 3 DEVELOPED DRAINAGE BASIN MAP ................................................. 12
FIGURE 4 SNOHOMISH COUNTY SOILS MAP ..................................................... 13
FIGURE 5 UPSTREAM/DOWNSTREAM TRIBUTARY AREA MAP ........................ 14
Sundstone SP 19-0117
October, 2019 Page 2
1. INTRODUCTION & SITE CLASSIFICATION
This document is intended to provide preliminary engineering information necessary to support
the preliminary short plat permit application submittal to the City of Edmonds for the new 2 lot
short plat proposed on this parcel. The current property is approximately 51,922 sf. Access to the
existing condos on this site is from an access easement to the northwest. The proposed access for
the new SFR will be directly off of 9' Ave N along the western property line.
The total area of disturbance including clearing and grading does not exceed % acres and the new
total impervious surfaces does exceed 3,550 sf. Therefore, this project is classified as a Category 1
Small Site Project. This classification was completed using figure 2-1 of the 2017 Storm water
Code Supplement to Edmonds Community Development Code Chapter 18.30. Due to the existing
soil conditions, on -site infiltration is not feasible for this project and dispersion will be the selected
LID BMP for this project where feasible. Refer to Section 6 of this report for a detailed feasibility
analysis. As a result, only minimum requirements 1-5 will be required to be reviewed and
addressed for this project.
This proposed project will create approximately 3,550 sf of new impervious surfaces including the
proposed srR and driveway. No impervious surfaces will be considered removed or replaced for
this project. All of the new impervious surfaces will be mitigated using on -site stormwater
management BMPs including dispersion and amended soils; both LID techniques. In addition,
another 3,550 sf of retrofit area will be mitigated on -site along the east side of proposed Lot 2 via
a level spreader trench. This will meet the requirements per ECDC 18.30.060.D.5.b.i.
The site is located at 1414 9th Ave N, Edmonds, WA 98020, and in Section 13, Township 27N,
Range 3E, Willamette Meridian. See Figure 1 - Vicinity Map..
Sundstone SP 19-0117
October, 2019 Page 3
2. STORMWATER SITE PLAN
As noted in Section 1 of this report this project is classified as a Category 1 Small Site Project.
Therefore, this drainage design has been prepared to address the requirements contained in the
City of Edmonds Stormwater Supplement and applicable handouts. This document is intended to
provide the supporting information to justify the BMPs used and to detail how the design of the
selected BIVIPs meet the required standards.
For this project some LID techniques were used to aid in minimizing the project's impacts to the
neighboring properties and downstream system. The new NPGIS & PGIS runoff will be dispersed
where feasible on -site and the soils within the proposed area of disturbance will be amended to
landscaping conditions as per BIVIP T5.13 out of the 2014 DOE SWMMWW. This is done to reduce
the stormwater runoff generated by the proposed impervious surfaces.
3. SWPPP NARRATIVE
Clearing, grading, and temporary erosion and sediment control plans will be prepared as part of
the final engineering drawings. However, since a construction site is dynamic it will be necessary
to reassess the erosion control BIVIP's during construction and install additional measures when
necessary.
Proposed temporary measures possible for this project will include the following BIVIP's:
Installation of stabilized construction entrance.
Retention of Existing Vegetation
Straw mulch, hydroseed or other mulching and planting method to stabilized unworked
areas.
Silt fencing if necessary
Permanent measures to reduce or eliminate erosion or water quality degradation will include the
following BIVIP's:
Paving all traffic areas (concrete/asphalt)
Permanent landscaping in pervious areas.
Limiting cut and fill slopes to 2:1 maximum and 3:1 maximum where exposed to standing
water.
Routine maintenance and inspection of the grounds and response to developing
problems.
The listed erosion control BIVIP's will be engineered for anticipated conditions in compliance with
City and DOE guidelines. With proper installation, maintenance and inspection the proposed
BMP's should result in minimal impact to the surrounding environment. The City retains the
authority by code to require additional measures should the existing BIVIPs prove insufficient.
Sundstone SP 19-0117
October, 2019 Page 4
A. SITE GRADING/EROSION CONTROL RISK ASSESSMENT
Area proposed to be cleared/worked: 9,000 sf = 0.21 acres
Average slope for the site (w/in the area of disturbance): 10%
Erosion Hazard of Soil Moderate
Critical Areas clownslope No
Site is upstream of an ESA Stream No
Based on the above information and the fact that the site will retain some existing vegetation and
construction site runoff will filter through the soil, and that if site conditions warrant, additional
BMP's can be implemented as corrective measures the Risk Category for this site is Low Risk.
B. SWPPP MINIMUM ELEMENTS
1: Mark Clearing Limits
The first step in the "Construction Sequence" included on the clearing and grading plan
sheets is for the limits of clearing to be flagged and to have construction fencing placed
along the limits prior to any other construction activity.
2: Establish Construction Access
The SWPPP calls for the proposed construction entrance to be installed as the second
step after the staking of clearing limits. A detail is provided on the plans.
3: Control Flow Rates
This project is below the thresholds requiring flow control for the project.
4: Install Sediment Controls
This site and SWPPP proposes to construct/maintain a construction entrance, retained
vegetation and silt fencing. These features are intended to minimize the opportunity for
sediment to leave the site via stormwater or on vehicles. The construction of these
features is one of the first items required in the "Construction Sequence". Mulch will also
be used on the exposed soil as necessary to limit erosion.
5: Stabilize Soils
The "Construction Sequence" calls for the stabilization of soils that remain unworked for
certain lengths of time based on the time of year. Stabilization techniques may include but
not limited.to mulching, plastic sheeting or hydroseeding, notes have been added to the
plan regarding protection for the stockpile area if necessary. A stockpile area has been
identified on the SWPPP and is setback a minimum of 25-feet from any down slope
property line.
6: Protect Slopes
.All disturbed.slopes on site during construction are required to be protected with mulch or
other means as specified in the construction sequence. No concentrated runoff or
significant amounts of sheet flow will be directed to new cut or fill slopes during
construction.
Sundstone SP 19-0117
October, 2019 Page 5
7: Protect Drain Inlets
No new or existing culverts are proposed or affected by this project.
8: Stabilize Channels and Outlets
No new channels or outlets are proposed for this site.
9: Control Pollutants
No outside chemicals are expected to be necessary for the construction of this project. All
vehicles working on and around the site would need to meet the State requirements for
emissions.
10: Control DeWatering
DeWatering will not be necessary for this project. However, the existing vegetation
retained on site would be available to spread any water from construction for disposal.
11: Maintain BMPs
The construction supervisor will be responsible for maintaining all BMPs during
construction and working with the City to relocate or add BMPs as necessary as site
conditions change.
12: Manage the Project
It will be the responsibility of the Contractor and Developer to manage this project and
coordinate with the City Inspector and Engineer.
Inspection and Monitoring:
Site inspections shall be done by a person who is knowledgeable in the principles and
practices of erosion and sediment control. The person must have skills to first assess the
site conditions and construction activities that could impact the quality of stormwater, and
second assess the effectiveness of erosion and sediment control measures used to
control the quality of stormwater discharges.
Whenever inspection and/or monitoring reveals that the BMPs identified in the
Construction SWPPP are inadequate, due to the actual discharge of or potential to
discharge a significant amount of any pollutant, appropriate BMPs or design changes shall
be implemented as soon as possible.
Maintaining an Updated Construction SWPPP:
The construction SWPPP shall be retained on -site or within reasonable access to the site.
The SWPPP shall be modified whenever there is a change in the design, construction,
operation, or maintenance at the construction site that has, or could have, a significant
effect on the discharge of pollutants to waters of the state.
The SWPPP shall be modified if, during inspections or investigations conducted by the
owner/operator, or the applicable local or state regulatory authority, it is determined that
the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater
discharges from the site. The SWPPP shall be modified as necessary to include
additional or modified BMPs designed to correct problems identified. Revisions to the
SWPPP shall be completed within seven days following inspection.
Sundstone SP 19-0117
October, 2019 Page 6
4. WATER POLLUTION SOURCE CONTROL
The City of Edmonds Stormwater Supplement and DOE Drainage manual was reviewed to
determine if the proposed land -use for this project required any site -specific source control BMPs
to be constructed. SFR projects are not listed as a proposed use that requires source control.
Therefore, no site/development specific source control BMPs are required for this project.
5. PRESERVATION OF NATURAL DRAINAGE SYSTEM
The runoff from the on -site basin drains to the west towards the western property line and the
adjacent R/W as sheet flow. It was determined that the runoff from the site improvements will be
dispersed on -site, the maximum extent feasible, or directly connected to the existing drainage
system in the R/W. Both the proposed roof & driveway will disperse flows over amend ed soils
when the required flow paths are available, otherwise roof downspouts will be collected and
directed to a perforated stubout connection before discharging to the existing drainage system
within 9th Ave N. This will allow the maximum amount of runoff to be treated and naturally
absorb into the on -site soils while not concentrating any of the flows. By not grading or
compacting most of the pervious surfaces to remain after construction in the area of disturbance a
maximum amount of site runoff from the developed project will be absorbed into the existing on -
site soils and remain as sheet flow as it leaves the site which will match the existing conditions.
6. ON -SITE STORMWATER MANAGEMENT
The on -site soils for this project have been mapped by the web soil survey as Alderwood Urban
Land Complex. This soil type is typically a till soil in urban/developed areas where the existing
ground has been disturbed/graded. Typically, the depth to the top of the till (hard pan) layer is
between 2-3 feet below the existing grade. The soil unit is gravelly ashy sandy loam. Refer to
Figure 4 to view Soils map. This project proposes to construct approximately 2,250 sf of new plus
replaced roof surfaces and/or walks.
Using the City of Edmonds Appendix A — On -Site Stormwater Management BMP Infeasibility
Criteria the following describes the BMP selection process for this project.
Lawn and Landscaped Areas:
Post-Con'structio'n'Soil Quality and Depth: This option was selected, and the specifications will be
provided on the future construction engineering plans.
Roofs (2,340 sf to be mitigated):
Full Dispersion: Not selected since the 65:10 required ratio could not be met for this project and
since the 100-foot retained/native vegetative flow path cannot be provided.
Downspout Full Infiltration:
Based on the disturbed nature of the site and the mapped soil type there is not more than 3-feet
of permeable soils available for this project. In addition, the project Geotech has prepared a
Sundstone SP 19-0117
October, 2019 Page 7
report based on their site investigations and found the long-term infiltration rate for the existing
soils to be less than 0.05"/hr which is well below the infeasibility rate for infiltration.
Bioretention or Rain Gardens:
Based on the disturbed nature of the site and the mapped soil type there is not more than 3-feet
of permeable soils available for this project and based on Geotechnical findings noted above.
Downspout Dispersion Systems:
SELECTED (where feasible) — No more than 700 sf of roof shall be directed to any one dispersion
system. Refer to Preliminary Development Plan
No further Roof BMP evaluation for feasibility is necessary.
Other Hard Surfaces:
Permeable Pavement:
Due to site grades it is necessary for much of the proposed driveway to be installed in a cut
condition which causes the bottom of the lowest permeable layer to be within I -foot of the
identified hard -pan layer and based on Geotechnical findings noted above.
Bio-Retention or Rain Gardens:
See discussion above.
Sheet Flow Dispersion:
SELECTED (to maximum extent feasible) — Refer to Preliminary Development Plan.
The roof will require a minimum of four splash blocks or level spreaders with additional locations
allowed as needed based on the final roof/gutter layout. Each splash block will provide a
minimum flow path of 50-feet over amended or natural vegetation/topsoil and level spreaders will
provide 25' flow paths.
A total of approximately 1,305 sf of PGIS is proposed for this project. The driveway will be graded
to allow sheet flow dispersion along the north side of the new surface. The runoff will then flow
over amended soils and vegetation to the maximum extent practical before being collected along
the east side of the existing 9th Ave N road surface where that is not possible.
Any other walks or patios would be designed the same to allow runoff to sheet flow off the
surface and spread over amended soils.
All permeable surfaces that are graded or compacted during construction will be amended using
-topsoil or�compost as provided in the specifications provided on sheet 6 of the plan set.
Sundstone SP 19-0117
October, 2019 Page 8
7. RUN-OFF TREATMENT
This project proposes to construct less than 5,000 sf of new PGIS and is therefore exempt from
any run-off treatment.
8. FLOW CONTROL
This project proposes to construct less than 5,000 sf of new impervious surfaces and is therefore
exempt from any flow control requirements.
9. WETLANDS PROTECTION
This project will not impact any wetland on -site or downstream of the project site.
Sundstone SP 19-0117
October, 2019 Page 9
10. OPERATIONS AND MAINTENANCE MANUAL
The Property Owner will be responsible for maintaining the stormwater and landscaping facilities
within this development. Included in this manual are checklists for each feature specific to this
project, Copies should be made of the checklists as necessary during routine inspections and
required maintenance. Specific problems can be recorded along with the appropriate action
taken.
These checklists are a guide for inspections and maintenance. The frequency of the
inspections/maintenance is identified in the left-hand column with the following abbreviations:
A = Annual (March or April preferred)
M = Monthly
S = After Major Storms (Use 1-inch in 24 hours as a guideline)
Routine inspections and maintenance will improve the long-term performance of the stormwater
facilities. If at any time you are unsure if a problem exists or how to address a specific problem,
contact a Professional Engineer.
Refer to Appendix A for a list of each facility to be maintained and the appropriate maintenance
checklist (To be provided with final engineering report).
Sundstone SP 19-0117
October, 2019 Page 10
APPENDIX A
Sundstone SP 19-0117
October, 2019 Page 11
A
NGA
Main Office
173 11 = 135" Ave NE, A-500
Woodinville, WA 98072
(425) 486-1669 - FAX (425) 481-25 10
December 21, 2018
Ms. Lindell Graham
1414 - 91 Avenue North
Edmonds, WA 98020
lindellg@.hotmail.com
NELSON GEOTeCHNICAL
AssociATEs, INC.
GF-oTECHNICAL ENGINEERS & GEoLoGjsTs
Geotechnical Engineering Evaluation
Sundstone Short Plat
1414 - 9' Avenue North
Edmonds, Washington
NGA File No. 1074518
Dear Ms. Graham:
Engineering -Geology Branch.
5526 Industry Lane, #2
East,Wenatcbee, WA 98802
(509) 665-7696 - FAX (509) 665-7692
We are pleased to submit the attached report titled "Geotechnical Engineering Evaluation — Sundstone
Short Plat — 1414 - 9th Avenue North — Edmonds, Washington." This report summarizes our
observations of the existing surface and subsurface conditions within the site, and provides general
recommendations for the proposed site development. Our services were completed in general accordance
with the proposal signed by you on November 18, 2018.
The level to gently west -sloping site is occupied by a multistory multifamily residential structure on the
eastern portion of the property, and is vacant on the western portion. The property is bordered to the
north by existing residential properties, to the west by 9th Avenue North, to the south by an easement
along Puget Drive (WA-524), and to the east by commercial development. We understand that the 1. 18-
acre parcel will undergo a short plat to create at least one additional residential parcel within the vacant
western portion, and that the Sundstone Condominium structure is intended to remain in the east. We
understand that stormwater generated within this site will be directed to on -site infiltration facilities if
feasible. Specific -grading -and stormwater.plans were. not available when this report was prepared, but
based on conversations with you, we understand that stormwater may be directed to on -site infiltration
facilities, if feasible. In addition to providing recommendations for the development of the new single-
family residence(s), we have been requested to evaluate the infiltration capacity of the site soils. The City
of Edmonds utilizes the 2014 WSDOE Stormwater Management Manual for Western Washington to
determine the design of infiltration facilities. According to this manual, on -site infiltration testing
consisting of the small Pilot Infiltration Test (PIT) is used to determine the long-term design infiltration
rates.
We performed four test pit explorations throughout the property, one of which we utilized for our small-
scale pilot infiltration testing (PIT). Our explorations indicated that the site was underlain by surficial
undocumented fill with competent, native soils at depth.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edm onds, Washington
NGA File No. 1074518
December 21, 2018
Summary — Page 2
It is our opinion that the proposed site development is feasible from a geotechnical engineering
standpoint, provided that our recommendations for site development are incorporated into project plans.
In general, the native soils underlying the site should adequately support the planned structures.
Foundations should be advanced through any loose soils down to the competent native bearing material
interpreted to underlie the site, for bearing capacity and settlement considerations. These soils should
generally be, encountered approximately two to three feet below the existing ground surface, based on our
explorations. If loose soils or undocumented fill are encountered in unexplored areas of the site,,they
should be removed and replaced with structural fill for foundation and pavement support. Final
stormwater plans have also not been developed, but we understand that on -site infiltration is being
considered for this site. Based on our onsite testing, it is our opinion that the onsite soils are not
conducive to traditional methods of stonnwater infiltration, however low -impact design systems may be
feasible. The subsurface soils generally consisted of surficial undocumented fill soils underlain by silty
fine to medium sand with varying amounts of gravel and iron -oxide weathering that we interpreted as
native glacial soils at relatively shallow depths. We recommend that any low impact stonnwater
infiltration systems be designed in accordance with the 2014 Department of Ecology Stormwater
Management Manual for Western Washington.
In the attached report, we have also provided general recommendations for site grading, slabs -on -grade,
structural fill placement, retaining walls, erosion control, and drainage. We should be retained to review
and comment on final development plans and observe the earthwork phase of construction. We also
recommend that NGA be retained to provide monitoring and consultation services during construction to
confirm that the conditions encountered are consistent with those indicated by the explorations, to provide
recommendations for design changes should the conditions revealed during the work differ from those
anticipated, and to evaluate whether or not earthwork and foundation installation activities comply with
contract plans and specifications.
It has been a pleasure to provide service to you on this project. Please contact us if you have any
questions regarding this report or require further information.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
Khaled M. Shawish, PE
Principal Engineer
TABLE OF CONTENTS
INTRODUCTION.............................................................................................................
I
I
SCOPE...............................................................................................................................
SITECONDITIONS .........................................................................................................
2
SurfaceConditions
2
.......................................................................................................
SubsurfaceConditions
2
..................................................................................................
HydrogeologicConditions ...........................................................................................
3
3
SENSITIVEAREA EVALUATION ...............................................................................
SeismicHazard
3
.............................................................................................................
ErosionHazard .............................................................................................................
4
CONCLUSIONS AND RECOMMENDATIONS ..........................................................
4
4
General.........................................................................................................................
ErosionControl ............................................................................................................
5
Site Preparation and Grading .......................................................................................
5
Temporary and Permanent Slopes ...............................................................................
6
7
Foundations..................................................................................................................
RetainingWalls ............................................................................................................
8
9
StructuralFill ................................................................................................................
Slab -on -Grade ..............................................................................................................
9
10
Pavements...................................................................................................................
10
Utilities.......................................................................................................................
10
SiteDrainage ..............................................................................................................
CONSTRUCTIONMONITORING .............................................................................
12
USEOF THIS REPORT ................................................................................................ 12
LIST OF FIGURES
Figure I — Vicinity Map
Figure 2 — Site Plan
Figure 3 — Soil Classification Chart
Figure 4 — Test Pit Logs
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
1414 _ 91h Avenue North
Edmonds,, Washington
INTRODUCTION
This report presents the results of our geotechnical engineering investigation and evaluation of the
planned Sundstone Short Plat Development project in the Edmonds, Washington. The project site is
located at 1414 _ 9th Avenue West, as shown on the Vicinity Map in Figure 1. The purpose of this study
is to explore and characterize the site's surface and subsurface conditions and to provide geotechnical
recommendations for the planned site development. For our use in preparing this report, we have been
provided with an undated and untitled preliminary site plan showing the existing and proposed conditions
within the site.
The property is currently occupied by a multi -level multi -family residential structure within the eastern
portion of the site, while the subject western portion of the site is undeveloped. We understand the
proposed developments within the site will include short platting the property and constructing a new
residential structure within the lower western parcel. Topography within the subject portion of the site
slopes gently from east to west. Vegetation generally consists of grass -covered yard areas and scattered
young to mature trees. Final development and grading plans have not been prepared at the time this
report was issued. Final stormwater plans have also not been developed, however, we understand that
storniwater may be directed to on -site infiltration systems, if feasible. The existing and proposed site
layout is shown on the Site Plan in Figure 2.
SCOPE
The purpose of this study is to explore and characterize the site surface and subsurface conditions, and
provide general recommendations for site development. Specifically, our scope of services includes the
following:
1 . Review available soil and geologic maps of the area.
2. Explore the subsurface soil and groundwater conditions within the site with track -
mounted backhoe-excavated test pits. Excavation services were provided by NGA.
3. Perform laboratory grain -size sieve analysis on soil samples, if necessary.
4. Provide recommendations for earthwork, foundation support, and slabs -on -grade.
5. Provide recommendations for temporary and permanent slopes.
6. Provide recommendations for pavement subgrade.
7. Provide recommendations for site drainage and erosion control.
,.8. Provide,our opinion on -the feasibility of infiltration for the onsite soils.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
NGA File No. 1074518
December 21, 2018
Page 2
9. Provide long-term design infiltration rates based on on -site Pilot Infiltration Testing (PIT)
per the 2014 WSDOE Manual. One test to be performed within each proposed property.
10. Provide recommendations for infiltration system installation.
11. Document the results of our findings, conclusions, and recommendations in a written
geotechnical report.
SITE CONDITIONS
Surface Conditions
The overall property consists 0 an approximately 1.18-acre parcel with a multi -family residential
structure within the eastern portion of the site and vacant undeveloped land to the west. We understand
the proposed improvements will consist of dividing the property into two parcels and constructing a
residential structure within the western parcel. The proposed western parcel is vegetated with grass lawn
and few scattered young to mature trees. The ground surface slopes gently from east to west. The subject
site is bound to the east by the multi -family structure, to the north by a residential property, to the south
by P I uget Drive, and to the west by 9'11 Avenue North. We did not observe surface water throughout the
site during our visit on December 3, 2018.
Subsurface Conditions
Geology: The site is mapped on the Geologic mgp of the Edmonds East and part of the Edmonds West
quadrangles, Washington, by James P. Minard (US Geological Survey, 1983). The site is mapped as till
and transitional beds (Qtu and Qtb, respectively). Till deposits generally consists of a compact non -sorted
mixture of clay, silt, sand, pebbles, and boulders. Transitional beds are described as thin bedded clay, silt,
and very fine to fine sand with some layers of peaty sand and gravel lower in the unit. Our explorations
typically encountered undocumented fill underlain by silty fine to medium sand with varying amounts of
gravel consistent with the description of native till deposits at depth.
Explorations: The subsurface conditions within the site were explored on December 3, 2018 by
excavating four, test, pits to approximate -depths in, the range of 4.0 to 5.5 feet below the existing ground
surface using a mini-trackhoe. The approximate locations of our explorations are shown on the Site Plan
in Figure 2. A geologist'from NGA was present during the explorations, examined the soils and geologic
conditions encountered, obtained samples of the different soil types, and maintained logs of the test pits.
The soils were visually classified in general accordance with the Unified Soil Classification System,
presented in Figure 3. The logs of our test pits are attached to this report and are presented as Figure 4.
We present a brief summary of the subsurface conditions in the following paragraphs, For a detailed
description of the subsurface conditions, the logs of the test pits should be reviewed.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 1074518
Sundstone Short Plat December 21, 2018
Edmonds, Washington Page 3
At the surface of each exploration we generally encountered 1.7 to 2.5 feet of dark brown to brown, silty
fine to medium sand with varying amounts of gravel, roots, and organics, which we interpreted as topsoil
and/or undocumented fill soils. Underlying the fill soils and topsoil we generally encountered medium
dense or better orange -brown to gray, silty fine to medium sand with varying amounts of gravel and iron -
oxide staining, which we interprete� as native till deposits at depth. Infiltration Pit I and Test Pits I
through 3 terminated at respective depths of 4.0, 5.0, 5.5, and 4.0 feet below the existing ground surface.
Hydrogeologic Conditions
We did not encounter groundwater within our explorations throughout the site. If groundwater is
encountered during construction we would interpret this as a perched groundwater condition. Perched
water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on
top of relatively low permeability materials. The more permeable soils consist of the topsoil/weathered
soils and undocumented fill. The low permeability soil consists of relatively silty native deposits.
Perched water does not represent a regional groundwater "table" within the upper soil horizons. Perched
water tends to vary spatially and is dependent upon the amount of rainfall. We would expect the amount
of perched groundwater to decrease during drier times of the year and increase during wetter periods.
SENSITIVE AREA EVALUATION
Seismic Hazard
We reviewed the 2018 International Building Code (IBC) for seismic site classification for this project.
Since competent�glaeial,soils are inferred to underlie the site at depth, the site conditions,best fit the IBC
description for Site Class D.
Table I below provides seismic design parameters for the site that are in conformance with the 2018
IBC, which specifies a design earthquake having a 2% probability of occurrence in 50 years (return
interval of 2,475 years), and the 2008 USGS seismic hazard maps.
Table 1 — 2018 IBC Seismic Design Parameters
Site Class
Spectral Acceleration
Spectral Acceleration
Site Coefficients
Design Spectral
at 0.2 sec. (g)
at 1.0 sec. (g)
Response
S,
Si
Parameters
Fa
F,
SDS
SDI
[_D7
1.278
0.501
1.000
1.5
0.852
The spectral response accelerations were obtained from the USGS Earthquake Hazards Program
Interpolated Probabilistic Ground Motion website (2008 data) for the project latitude and longitude.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation NGA File No. 10745 18
Sundstone Short Plat December 21, 2018
Edmonds, Washington Page 4
The site is located within the South Whidbey Island Fault Zone (SWIFZ): an active, shallow region of
seismicity within central Puget Sound stretching from the Strait of Juan de Fuca to North Bend.
Information published in 2013 by the Washington State Department of Natural Resources suggests the
SWIFZ last ruptured less than 2,700 years ago, and that the fault zone can produce a M7.5 earthquake. In
our opinion, the possibility of faulting ground rupture caused by this fault zone is considered low.
Hazards associated with seismic activity include liquefaction potential and amplification of ground
motion. Liquefaction is caused by a rise in pore pressures in a loose, fine sand deposit beneath the
groundwater table. It is our opinion that the medium dense or better deposits interpreted to underlie the
site have a low potential for liquefaction or amplification of ground motion.
Erosion Hazard
The criteria used for determination of the erosion hazard for affected areas include soil type, slope
gradient, vegetation cover, and groundwater conditions. The erosion sensitivity is related to vegetative
cover and the specific surface soil types, which are related to the underlying geologic soil units. The.Soil
Surypy of Snohomish Counjy Area, Washington, by the Natural Resources Conservation Service (NRCS)
was reviewed to determine the erosion hazard of the on -site soils. The surface soils for this site were
mapped as Alderwood-Urban land complex, 2 to 8 percent slopes. The erosion hazard for this material is
listed as slight. This site is relatively level to gently sloping and there are no steep slopes on the property.
It is our opinion that the erosion hazard for site soils should be low in areas where the site is not
disturbed.
CONCLUSIONS AND RECOMMENDATIONS
General
It is our opinion that the site planned development is feasible from a geotechnical standpoint. Our
explorations indicated that the site is generally underlain by competent native bearing soils at relatively
shallow depths. The native soils encountered at depth should provide adequate support for foundation,
slab, and pavement loads. We recommend that the planned structure be designed utilizing shallow
foundations. Footings should extend through any loose soil or undocumented fill soils and be founded on
the underlying medium dense or better native bearing soil, or structural fill extending to these soils. The
medium dense or better native glacial soils should typically be encountered approximately two to three
feet below the existing surface, based on our explorations. We should note that localized areas of deeper
unsuitable soils and/or undocumented fill could be encountered at this site. This condition would require
additional excavations in foundation, slab, and pavement areas to remove the unsuitable soils.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
NGA File No. 1074518
December 21, 2018
Page 5
Based on the results of our infiltration testing and soil explorations throughout the site, it is our opinion
that the onsite native soils are not conducive for traditional methods of stormwater infiltration. This is
further discussed in the Site Drainage section of this report.
Erosion Control
The erosion hazard for the on -site soils is interpreted to be slight for exposed soils, but actual erosion
potential will be dependent on how the site is graded and how water is allowed to concentrate. Best
Management Practices (BMPs) should be used to control erosion. Areas disturbed during construction
should be protected from erosion. Erosion control measures may include diverting surface water away
from the stripped or disturbed areas. Silt fences and/or straw bales should be erected to prevent muddy
water from leaving the site. Disturbed areas should be planted as soon as practical and the vegetation
should be maintained until it is established. The erosion potential of areas not stripped of vegetation
should be low.
Site Preparation and Grading
After erosion control measures are implemented, site preparation should consist of stripping the topsoil,
undocumented fill and loose soils from foundation, slab, pavement areas, and other structural areas, to
expose medium dense or better native bearing soils. The stripped soil should be removed from the site or
stockpiled for later use as a landscaping fill. Based on our observations, we anticipate stripping depths of
two to three feet, depending on the specific locations. However, additional stripping may be required if
areas of deeper undocumented fill and/or loose soil- are encountered in unexplored areas of the site.
After site stripping, if the exposed subgrade is deemed loose, it should be compacted to a non -yielding
condition and then proof -rolled with a heavy rubber -tired piece of equipment. Areas observed to pump or
weave during the proof -roll test should be reworked to structural fill specifications or over -excavated and
replaced with properly compacted structural fill or rock spalls. if loose soils are encountered in the
pavement areas, the loose soils should be removed and replaced with rock spalls or granular structural fill.
If significant surface water flow is encountered during construction, this flow should be diverted around
areas to be developed, and the exposed subgrades should be maintained in a semi -dry condition.
If wet conditions are encountered, alternative site stripping and grading techniques might be necessary.
These could include using large excavato rs equipped with wide tracks and a smooth bucket to complete
site grading and covering exposed subgrade with a layer of crushed rock for protection. If wet conditions
are encountered or construction is attempted in wet weather, the subgrade should not be compacted as this
could cause further subgrade disturbance. In wet conditions it may be necessary to cover the exposed
subgrade with a layer of crushed rock as soon as it is exposed to protect the moisture sensitive soils from
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
NGA File No. 1074518
December 21, 2018
Page 6
disturbance by machine or foot traffic during construction. The prepared subgrade should be protected
from construction traffic and surface water should be diverted around areas of prepared subgrade.
The site soils are considered to be moisture -sensitive and will disturb easily when wet. We recommend
that construction take place during the drier summer months if possible. However, if construction takes
place during the wet season, additional expenses and delays should be expected due to the wet conditions.
Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades,
construction traffic areas, and paved areas prior to placing structural fill. Wet weather grading will also
require additional, erosion control and site drainage measures. Some of the on -site soils may be suitable
for use as structural fill, depending on the moisture content of the soil at the time of construction. NGA
should be retained to evaluate the suitability of all on -site and imported structural fill material during
construction.
Temporary and Permanent Slopes
Temporary cut slope stability is a function of many factors, including the type and consistency of soils,
depth of the cut, surcharge loads adjacent to the excavation, length of time a cut remains open, and the
presence of surface or groundwater. It is exceedingly difficult under these variable conditions to estimate
a stable, temporary, cut slope angle. Therefore, it should be the responsibility of the contractor to
maintain safe slope configurations at all times as indicated in OSHA guidelines for cut slopes -
The following information is provided solely for the benefit of the owner and other design consultants and
should not be construed to imply that Nelson Geotechnical Associates, Inc. assumes responsibility for job
site safety. Job site safety is the sole responsibility of the project contractor.
For planning purposes, we recommend that temporary cuts in the upper undocumented fill soils be no
steeper than 2 Horizontal to 1 Vertical (211: IV). Temporary cuts in the competent native soils at depth
should be no steeper than I.5H:IV. If significant groundwater seepage or surface water flow were
encountered, we would expect that flatter inclinations would be necessary. We recommend that cut
slopes be protected from erosion. The slope protection measures may include covering cut slopes with
plastic sheeting and diverting surface runoff away from the top of cut slopes. We do not recommend
vertical slopes for cuts deeper than four feet, if worker access is necessary. We recommend that cut slope
heights and inclinations conform to appropriate OSHA/WISHA regulations
Permanent cut and fill slopes should be no steeper than 2H: IV. However, flatter inclinations may be
required in areas where loose soils are encountered. Permanent slopes should be vegetated and the
vegetative cover maintained until established.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmondsi, Washington
Foundations
NGA File No. 1074518
December 21, 2018
Page 7
Conventional shallow spread foundations should be placed on medium dense or better native bearing
soils, or be supported on structural fill or rock spalls extending to those soils. Medium dense soils should
be encountered approximately two to three feet below ground surface based on our explorations. Where
undocumented fill or less dense soils are encountered at footing bearing elevation, the subgrade should be
over -excavated to expose suitable bearing soil. The over -excavation may be filled with structural fill, or
the footing may be extended down to the competent native bearing soils. If footings are supported on
structural fill, the fill zone should extend outside the edges of the footing a distance equal to one half of
the depth of the over -excavation below the bottom of the footing.
Footings should extend at least 18 inches below the lowest ad acent finished ground surface for frost
i
protection and bearing capacity considerations. Foundations should be designed in accordance with the
2018 IBC. Footing widths should be based on the anticipated loads and allowable soil bearing pressure.
Water should not be allowed to accumulate in footing trenches.. All loose or disturbed soil should be
removed from the foundation excavation prior to placing concrete.
For foundations constructed as outlined above, we recommend an allowable design bearing pressure of
not more than 2,000 pounds per square foot (psf) be used for the design of footings founded on the
medium dense or better native bearing soils or structural fill extending to the competent native bearing
material. The foundation bearing soil should be evaluated by a representative of NGA. We should be
consulted if higher bearing pressures are needed. Current UBC guidelines should be used when
considering increased allowable bearing pressure for short-term transitory wind or seismic loads.
Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less
than 1 -inch total and 1/2-inch differential between adjacent footings or across a distance of about 20 feet,
based on our experience with similar projects.
Lateral loads may be resisted by friction on the base of the footing and passive resistance against the
subsurface portions of the foundation. A coefficient of friction of 0.35 may be used to calculate the base
friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a
triangular equivalent fluid pressure distribution. An equivalent fluid density of 200 pounds per cubic foot
(pcf) should be used for passive resistance design for a level ground surface adjacent to the footing. This
level surface should extend a distance equal to at least three times the footing depth. These recommended
values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and
passive resistance, respectively. To achieve this value of passive resistance, the foundations should be
poured "neat" against the native medium dense soils or compacted fill should be used as backfill against
the front of the footing. We recommend that the upper one foot of soil be neglected when calculating the
passive resistance.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
Retaining Walls
NGA File No. 1074518
December 21, 2018
Page 8
Specific grading plans for this project were not available at the time this report was prepared, but
retaining walls may be incorporated into project plans. In general, the lateral pressure acting on
subsurface retaining walls is dependent on the nature and density of the soil behind the wall, the amount
of lateral wall movement which can occur as backfill is placed, wall drainage conditions, and the
inclination of the backfill. For walls that are free to yield at the top at least one thousandth of the height
of the wall (active condition), soil pressures will be less than if movement is limited by such factors as
wall stiffness or bracing (at -rest condition). We recommend that walls supporting horizontal backfill and
not subjected to hydrostatic forces, be designed using a triangular earth pressure distribution equivalent to
that exerted by a fluid with a density of 40 pcf for yielding (active condition) walls, and 60 pcf for non -
yielding (at -rest condition) walls. A seismic design loading of 8H should also be included in the wall
design, where H represents the total height of the wall.
These recommended lateral earth pressures are for a drained granular backfill and are based on the
assumption of a horizontal ground surface behind the wall for a distance of at least the height of the wall,
and do not account for surcharge loads. Additional lateral earth pressures should be considered for
surcharge loads acting adjacent to walls and within a distance equal to the height of the wall. This would
include the effects of surcharges such as traffic loads, floor slab loads, slopes, or other surface loads. We
could consult with the structural engineer regarding additional loads on retaining walls during final
design, if needed.
The lateral pressures on walls may be resisted by friction between the foundation and subgrade soil, and
by passive resistance acting on the below -grade portion of the foundation. Recommendations for
frictional and passive resistance to lateral loads are presented in the Foundations subsection of this
report.
All wall backfill. should be well compacted as outlined in the Structural Fill subsection of this report,
Care should be taken to prevent the buildup of excess lateral soil pressures due to over -compaction of the
wall backfill. This can be accomplished by placing wall backfill in 8-inch loose lifts and compacting the
backfill with small, hand -operated compactors within a distance behind the wall equal to at least one-half
the height of the wall. The thickness of the loose lifts should be reduced to accommodate the lower
compactive energy of th& hand -operated equipment. The recommended level of compaction should still
be maintained.
Permanent drainage systems should be installed for retaining walls. Recommendations for these systems
are found in the Subsurface Drainage subsection of this report. We recommend that we be retained to
evaluate the proposed wall drain backfill material and observe installation of the drainage systems.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
Structural Fill
NGA File No. 1074518
December 21, 2018
Page 9
General: Fill placed beneath foundations, pavement, or other settlement -sensitive structures should be
placed as structural fill. Structural fill, by definition, is placed in accordance with prescribed methods and
standards, and is monitored by an experienced geotechnical professional or soils technician. Field
monitoring procedures would include the performance of a representative number of in -place density tests
to document the attaim-nent of the desired degree of relative compaction. The area to receive the fill
should be suitably prepared as described in the Site Preparation and Grading subsection prior to
beginning fill placement.
Materials: Structural fill should consist of a good quality, granular soil, free of organics and other
deleterious material, and be well graded to a maximum size of about three inches. All-weather fill should
contain no more than five -percent fines (soil finer than U.S. No. 200 sieve, based on that fraction passing
the U.S. 3/4-inch sieve). Some of the more granular on -site soils may be suitable for use as structural fill,
but this will be highly dependent on the moisture content of these soils at the time of construction. We
should be retained to evaluate all proposed structural fill material prior to placement.
Fill Placement: Following subgrade preparation, placement of structural fill may proceed. All filling
should be accomplished in uniform lifts up to eight inches thick. Each lift should be spread evenly and be
thoroughly compacted prior to placement of subsequent li fts. All structural fill underlying building areas
and pavement subgrade should be compacted to a minimum of 95 percent of its maximum dry density.
Maximum dry density, in this report, refers to that density as determined by the ASTM D-1557
Compaction Test procedure. The moisture content of the soils to be compacted should be within about
two percent of optimum so that a readily compactable condition exists. It may be necessary to over -
excavate and remove wet soils in cases where drying to a compactable condition is not feasible. All
compaction should be accomplished by equipment of a type and size sufficient to attain the desired degree
of compaction and should be tested.
Slab -on -Grade
Slabs -on -grade should be supported on subgrade soils prepared as described in the Site Preparation and
Grading subsection of this report. We recommend that all floor slabs be underlain by at least six inches
of free -draining gravel with less than three percent by weight of the material passing Sieve 4200 for use
as a capillary break. We recommend that the capillary break be hydraulically connected to the footing
drain system to allow free drainage from under the slab. A suitable vapor barrier, such as heavy plastic
sheeting (6-mil minimum), should be placed over the capillary break material. An additional 2-inch-thick
moist sand layer may be used to cover the vapor barrier. This sand layer may be used to protect the vapor
barrier membrane and to aid in curing the concrete.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
Pavements
NGA File No. 1074518
December 21, 2018
Page 10
Pavement subgrade preparation and structural filling where required, should be completed as
recommended in the Site Preparation and Grading and Structural Fill subsections of this report. The
pavement subgrade should be proof -rolled with a heavy, rubber -tired piece of equipment, to identify soft
or yielding areas that require repair. The pavement section should be underlain by a minimum of six
inches of clean granular pit run. We should be retained to observe the proof -rolling and recommend
repairs prior to placement of the asphalt or hard surfaces.
Utilities
We recommend that underground utilities be bedded with a minimum six inches of pea gravel prior to
backfilling the trench with on -site or imported material. Trenches within settlement sensitive areas
should be compacted to 95% of the modified proctor as described in the Structural Fill subsection of this
report. Trenches located in non-structural areas should be compacted to a minimum 90% of the
maximum dry density. The trench backfill compaction should be tested.
Site Drainage
Infiltration: We conducted a Small PIT within Infiltration Pit 1, located within the northwest portion of
the site as shown on the attached Schematic Site Plan in Figure 2. The test was conducted within a pit
that measured 4.0-feet long by 3.0-feet wide by 4.0-feet deep. The pit was filled with 12-inches of water
at the beginning of the day and we began the soaking period of the PIT for approximately 6 hours. At this
time, the water flow rate into the hole was monitored with a Great Plains Industries (GPI) TM 075 water
flow meter for the pre-soak period.
After the 6-hour soaking period was completed, the water level was maintained at approximately 12-
inches for one hour for the steady-state period. The flow rate for Infiltration Pit I stabilized at 0.02
gallons per minute (1.20 gallons per hour). This equated to an approximate infiltration rate of 0.182
inches per hour. The water was shut off after the steady-state period and monitored at least every 15
minutes for one hour. After 60 minutes, the water level within the pit dropped approximately 0.125
inches, resulting in a measured infiltration rate of 0. 12 5 inch per hour.
In accordance with the Table 3.5 of the Department of Ecology 2014 SVRvIN4WW, correction factors of
0.8, 0.5,,and,0.9 for CFv,,CFt, Urn, respectively were applied to the field measured infiltration rate of
0. 125 inches per hour, obtained from the falling -head portion of the testing in Infiltration Pit 1. A total
correction factor of 0.36 was applied to the measured field infiltration rate obtained from the falling head
portion of the test to determine the long-term design infiltration rate.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
NGA File No. 1074518
December 21, 2018
Page 11
Using the above correction factor, we calculated a long-term design infiltration rate of approximately
0.045 inches per hour. in our opinion, a long-term design infiltration rate of 0.045 inches per hour could
be utilized to design low -impact infiltration systems, such as rain gardens, bioswales, or permeable
pavements within the native, silty fine to medium sand with gravel found on this site at depth. We
recommend these systems be sized and designed in accordance with the 2014 Department of Ecology
Stormwater Management Manual for Western Washington and in conjunction with the provided long-
term design infiltration rate of 0.045 inches per hour. Additionally, due to the very low infiltration rate we
recommend incorporating an overflow component into any infiltration systems within the site, which
should be directed towards an approved point of discharge.
We recommend that any proposed infiltration systems be placed as to not negatively impact any proposed
or existing nearby structures and also meet all required setbacks from existing property lines, structures,
and sensitive areas as discussed in the drainage manual. In general, infiltration systems should not be
located within proposed fill areas within the site associated with site grading or retaining wall backfill as
such condition could lead to failures of the placed fills and/or retaining structures. We should be retained
to evaluate the infiltration system design and installation during construction.
Surface Drainage: The finished ground surface should be graded such that stormwater is directed to an
approved stormwater collection system. Water should not be allowed to stand in any areas where
footings, slabs, or pavements are to be constructed. Final site grades should allow for drainage away from
the residences. We suggest that the finished ground be sloped at a minimum gradient of three percent, for
a distance of at least 10 feet away from the residences. Surface water should be collected by permanent
catch basins and drain lines, and be discharged into an approved discharge system.
Subsurface Drainage: If groundwater is encountered during construction, we recommend that the
contractor slope the bottom of the excavation and collect the water into ditches and small sump pits where
the water can be pumped out and routed into a permanent storm drain.
We recommend the use of footing drains around the structures. Footing drains should be installed at least
one foot below planned finished floor elevation. The drains should consist of a minimum 4-inch-
diameter, rigid, slotted or perforated, PVC pipe surrounded by free -draining material wrapped in a filter
fabric. We recommend that the free -draining material consist of an 18-inch-wide zone of clean (less than
three -percent fines), granular material placed along the back of walls. Pea gravel is an acceptable drain
material. The free -draining material should extend up the wall to one foot below the finished surface.
The top foot of backfill should consist of impermeable soil placed over plastic sheeting or building paper
to minimize surface water or fines migration into the footing drain. Footing drains should discharge into
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmondsj Washington
NGA File No. 1074518
December 21, 2018
Page 12
tightlines leading to an approved collection and discharge point with convenient cleanouts to prolong the
useful life of the drains. Roof drains should not be connected to wall or footing drains.
CONSTRUCTION MONITORING
We should be retained to provide construction monitoring services during the earthwork phase of the
project to evaluate subgrade conditions, temporary cut conditions, fill compaction, and drainage system
installation.
USE OF THIS REPORT
NGA has prepared this report for Ms. Lindell Graham and her agents, for use in the planning and design
of the development on this site only. The scope of our work does not include services related to
construction safety precautions and our recommendations are not intended to direct the contractors'
methods, techniques, sequences, or procedures, except as specifically described in our report for
consideration in design. There are possible variations in subsurface conditions between the explorations
and also with time. Our.report, conclusions, and interpretations should not be construed as a warranty of
subsurface conditions, A contingency for unanticipated conditions should be included in the budget and
schedule.
We, recommend that NGA be retained to provide monitoring and consultation services during
construction to confirm that the conditions encountered are consistent with those indicated by the
explorations, to provide recommendations for design changes should the conditions revealed during the
work differ from those anticipated, and to evaluate whether or not earthwork and foundation installation
activities comply With contract plans and specifications. We should be contacted a minimum of one week
prior to construction activities and could attend pre -construction meetings if requested.
Within the limitations of scope, schedule, and budget, our services have been performed in accordance
with generally accepted geotechnical engineering practices in effect in this area at the time this report was
prepared. No other warranty, expressed or implied, is made. Our observations, findings, and opinions are
a means to identify and reduce the inherent risks to the owner.
NELSON GEOTECHNICAL ASSOCIATES, INC.
Geotechnical Engineering Evaluation
Sundstone Short Plat
Edmonds, Washington
NGA File No. 1074518
December 21, 2018
Page 13
It has been a pleasure to provide service to you on this project. If you have any questions or require
further information, please call.
Sincerely,
NELSON GEOTECHNICAL ASSOCIATES, INC.
". /w/ I
Alex B. Rinaldi, GIT
Staff Geologist H
Maher A. Shebl, Phl), PE, M.ASCE
Senior Engineer
ABR:MAS:dy
Four Figures Attached
NELSON GEOTECHNICAL ASSOCIATES, INC.
VICINITY MAP
Not to Scale
M.......
.....
. ....... ........ . ... . .. ..... ..
Project
Site
. . .... ..... ...
r a
. ....... .
Maplewood Rock. a
&
Ed ds
Eleme
t*y :School:
F
1 VWwfatw Way
. ...
..........
A
L......
... . . .
..... ..... .
..........
.. . ...... .. ........ .. .
. . . .
Methodist Church ... . .....
. .............
THE BOWL.
L:
. ....... . ...
....... ....... :'d.Q'r EDMO-1406
..........
sv"
Z
Y.
Edmonds, WA
Project Number NELSON GEOTECHNICAL No. Date Revision By ICK
I
ASSOCIATES, INC. C,
1074518 Graham Short Plat N�GA 1 12/5/18 Original DPN ABR
GEOTECHNICAL ENGINEERS.,&. GEOLOGISTS
Vicinity Map dInvIlleomce East Wenatch. Ofte
Figure 1 1731 WM35th Ava. NE, A-500 5526 Industry,Lane, #2
W..dJ I � East Wenatch- WA 98802
`il �'WA 98072
�425) 486-1669 1 F— 481-2510 --I—gs.teh.— (509) 665-76961 F- 665-7692
0 (D
z
(D (31
co
C7
(D
G)
U) a)
;q: :A
(D
-b
0
[OF
J
.... . . ....
z
4
>
9 n <
J (D
.0 11 >
z
M
z
M
zm > r
0
0 z
MW M
6 0
7 M -i
v M
V: n
"Flo
II.-. r
9 0 n z
o U,
H,g? -I >
1A r
LEGEND
z
P Property line
INF-1
0 Number and approximate
location of infiltration test pit
0 111-1
Number and approximate
o w
location of test pit
>
Ca
X Referenc Site an based on an undated plan ti
17_2L_
MiMcornDanv\2018 NGA Project Foldersx 745-18 Grharn SP FdMonds\Drafting\SP.dwg
Site Plan
.140.00'
pf i 44
Approximate
Location of
Proposed Residence,,'
.140.60
20.00T
br—
to
t
TP-2
.
. . .
. . . . . .
196th St NW
0 30 60
Scale: 1 inch = 30 feet
I
UNIFIED SOIL CLASSIFICATION SYSTEM
GROUP
MAJOR DIVISIONS
GROUPNAME
SYMBOL
CLEAN
GW
WELL -GRADED, FINE TO COARSE GRAVEL
COARSE-
GRAVEL
GRAVEL
GP
POORLY -GRADED GRAVEL
GRAINED
MORE THAN 50 %
GRAVEL
GM
SILTY GRAVEL
OF COARSE FRACTION
SOILS
RETAINED ON
NO. 4 SIEVE
WITH FINES
GC
CLAYEY GRAVEL
SAND
CLEAN
SW
WELL -GRADED SAND, FINE TO COARSE SAND
SAND
SP
POORLY GRADED SAND
MORE THAN 50 %
MORE THAN 50 %
RETAINED ON
NO. 200 SIEVE
OF COARSE FRACTION
SAND
Sm
SILTY SAND
PASSES NO. 4 SIEVE
SC
CLAYEY SAND
WITH FINES
FINE -
SILT AND CLAY
ML
SILT
INORGANIC
CL
CLAY
GRAINED
LIQUID LIMIT
LESS THAN 50 %
ORGANIC
OL
ORGANIC SILT, ORGANIC CLAY
SOILS
SILT AND CLAY
MH
SILT OF HIGH PLASTICITY, ELASTIC SILT
INORGANIC
MORE THAN 50 %
PASSES
LIQUID LIMIT
CH
CLAY OF HIGH PLASTICITY, FAT CLAY
NO. 200 SIEVE
50 % OR MORE
ORGANIC
OH
ORGANIC CLAY, ORGANIC SILT
HIGHLY ORGANIC SOILS
PT
PEAT
NOTES:
1) Field classification is based on visual SOIL MOISTURE MODIFIERS:
examination of soil in general Dry - Absence of moisture, dusty, dry to
accordance with ASTM D 2488-93. the touch
2) Soil classification using laboratory tests Moist - Damp, but no visible water.
is based on ASTM D 2488-93.
3) Descriptions of soil density or Wet - Visible free water or saturated,
usually soil is obtained from
consistency are based on below Water table
interpretation of blowcount data,
visual appearance of soils, and/or
test data.
Project Number
NELSON GEOTECHNICAL
No.
Date
Revision
By
CK
1074518
Graham Short Plat
'-�N�GA ASSOCIATES, INC.
1
12/5118
Original
DPN
ABR
Soil Classification,rChart
GEOTECHNICAL ENGINEERS & GEOLOGISTS
Figure 3
MdWille Ofte East Wenatchee Office
W311 _135th Ave. NE, A-500 lnd�.try L—, #2
.5526
Wc A 1112 E tWen,thee,WA98802
141�14=M:481-2510 �.nelsongeotechxorn (509) 665-76961 Fax: 665-7692
LOG OF EXPLORATION
DEPTH(FEET) Usc SOIL DESCRIPTION
INFILTRATION PIT
ONE
0.0-0.8
GRASS UNDERLAIN BY DARK BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, ROOTS,
AND ORGANICS (LOOSE TO MEDIUM DENSE, MOIST) (TOPSOIL)
0.8-2.0
ORANGE -BROWN, SILTY FINE TO MEDIUM SAND WITH GRAVEL, WOOD DEBRIS, AND ROOTS
(LOOSE TO MEDIUM DENSE, MOIST) (ELLIL
2.0-4.0
sm GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL (MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS NOT COLLECTED
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 4.0 FEET ON 12/3/2018
TEST PIT ONE
0.0-2.5
DARK BROWN, ORGANIC -RICH SILTY FINE TO MEDIUM SAND WITH GRAVEL AND ROOTS
(LOOSE TO MEDIUM DENSE, MOIST) (TOPSOIL)
2.5-5.0
SM GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE IRON -OXIDE STAINING
(MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS COLLECTED AT 4.0 FEET
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 5.0 FEET ON 12/3/2018
TEST PIT TWO
0.0-1.7
DA RK BROWN TO BROWN, ORGANIC -RICH SILTY FINE TO MEDIUM SAND WITH GRAVEL AND
ROOTS (LOOSE TO MEDIUM DENSE, MOIST) (TOPSOIL)
1.7-5.5
SM ORANGE -BROWN TO GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL, TRACE IRON -OXIDE
STAINING, AND ROOTS (MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS NOT COLLECTED
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 5.5 FEET ON 12/3/2018
TEST PIT THREE
0.0-1.0
DARK BROWN TO ORANGE -BROWN, ORGANIC -RICH SILTY FINE TO MEDIUM SAND WITH
GRAVEL AND ROOTS (LOOSE TO MEDIUM DENSE, MOIST) (TOPSOILLFiLL)
1.0-4.0
SM LIGHT BROWN TO GRAY, SILTY FINE TO MEDIUM SAND WITH GRAVEL AND TRACE IRON -OXIDE
STAINING (MEDIUM DENSE TO DENSE, MOIST)
SAMPLE WAS NOT COLLECTED
GROUNDWATER SEEPAGE WAS NOT ENCOUNTERED
TEST PIT CAVING WAS NOT ENCOUNTERED
TEST PIT WAS COMPLETED AT 4.0 FEET ON 12/3/2018
ABR:KMS NELSON GEOTECHNICAL ASSOCIATES, INC.
FILE NO 1074518
FIGURE 4